French Patent # 575,191

This patent describes Antoine Audouard’s Le Crack design of racing derailleur. Unlike his earlier design (French patent # 425,800), the Audouard Le Crack was a conventional mechanism in that the derailleur moved laterally the the freewheel cogs did not.

The derailleur itself was a somewhat crude affair, moved sideways by a crude lever. However this basic design allowed top and bottom normal options - and the top normal option pre-dated the rather similar Simplex bell-crank design by nearly a decade.